I need something called a "rusty helmet" to forge a mod item, but can't find it anywhere in the world or even on a console command item code list. If anyone knows anything about this, I'd like to know.

I just used the "help" command to see if something showed up with the keyword "rusty". None of the items were a helmet, or even armor for that matter. So, it's likely not an item found in vanilla Skyrim.